Growing numbers of teenagers are being forced to drop GCSEs in religious studies because of the introduction of new-style league tables that prioritise other disciplines, it was claimed.

In some schools, pupils are no longer allowed to take RE at all in the last two years of secondary education.

It is also feared that an expansion of independent academies – state schools run free of local authority control – is leading to rising numbers of schools dropping locally-agreed syllabuses in the subject.

The comments by the Religious Education Council of England and Wales were made despite claims of strong backing for the subject.

A survey of 1,800 adults – published by the council tpday – shows that more than half of people back compulsory lessons in RE up to the age of 16. Only a third said it should not be mandatory, it was revealed.

It comes as MPs and peers prepare to attend the first meeting of the newly-formed all-party parliamentary group for RE on Monday – established to raise awareness of the importance of the subject in schools.

John Keast, chairman of the RE Council, said the group was necessary to counter concerns that the subject was becoming increasingly marginalised by Coalition reforms to education.

This includes a Government decision to exclude RE from the English Baccalaureate – a new school leaving certificate that rewards pupils gaining good GCSE grades the five core academic disciplines of maths, English, science, foreign languages and either history or geography.

It is feared that this is leading to a decline in the number of schools offering the subject at GCSE level.

Mr Keast said: “There have been a number of unintended consequences for RE as a result of changes made by the Government.

“We are concerned that by prioritising other subjects, schools will discourage pupils from sitting GCSEs in RE and that will have a ripple effect for younger age groups. If a school is not really promoting RE as a subject at GCSE and A-level then specialist teachers are going to be discouraged from joining and that is only going to impact on how the subject is delivered for other pupils.”

Currently, RE is compulsory in primary and secondary schools but is not included in the National Curriculum. Instead, syllabuses are drawn up by local panels of experts and faith leaders in each council area to reflect the religious make-up of different communities.

But Mr Keast warned that many academy schools – with complete freedom from local authority control – could drop syllabuses, “undermining RE and making for more inconsistent teaching of the subject”.

Rabbi Dr Jonathan Romain, chairman of the Accord Coalition, which campaigns against selection by religion in schools, said RE should be added to the National Curriculum to ensure more uniform provision across the country.

“By all means let certain schools, if they so wish, teach more on one particular faith, but only after their pupils have had a thorough grounding in people all faiths and those of none,” he said. “Britain today is a multi-faith society but we don't want that to become a multi-fractious society.”

A Department for Education spokesman said: "RE remains a statutory part of the wider school curriculum for every single student up to 16. It's rightly down to schools themselves to judge how it is taught and how it fits into wider school life.

"The English Baccalaureate will not prevent any school from offering RE GCSEs. We have been clear that pupils should take the GCSEs that are right for them and that we look to teachers and parents to help pupils make the right learning choice."